The present invention relates generally to power converters, and more particularly to a control circuit for a phase-controlled rectifier or for an inverter.
One prior type of control circuit for a power converter is disclosed in Bailey et al U.S. Pat. No. 4,152,758. This patent discloses a control for a phase-controlled rectifier system for converting single-phase AC power into DC power. The control includes controlled rectifiers which are operated by switching signals generated in part by a ramp generator synchronized to an AC input waveform, with the ramp signal from the ramp generator being compared with a reference signal. The reference signal is disclosed as being an error voltage representing the difference between a desired voltage at the output of the rectifier and a commanded voltage.
Griess U.S. Pat. No. 3,986,047 discloses circuitry for generating switching signals for a phase-controlled regulator. Multiple ramp generators, one for each phase, generate ramp signals, each of which is compared with an error voltage to produce gating signals for a controlled rectifier.
A control system for controlling switches in a polyphase inverter is disclosed in Glennon Ser. No. 534,170, filed Sept. 19, 1983, and assigned to the assignee of the instant application. This control system utilizes a single pulse width modulator which generates a pulse width modulation waveform. This waveform is coupled to three-phase logic circuitry for developing switching signals for switches in the polyphase inverter. The pulse width modulator receives a triangle wave and an error signal, with the pulse width modulation waveform being a function of the level of the error signal and the frequency of the triangle wave.